This invention relates to a deflectable transducer mounting assembly and, more particularly, to such a mounting assembly which is particularly adapted for use in helical type video tape recorders (HVTR) which permits a previously recorded track of video information to be scanned accurately during special playback modes of operation, such as stop, slow motion, and reverse modes of operation.
Helical-type video tape recorders are known wherein video signals are recorded in, for example, successive fields in consecutive tracks which are arranged obliquely across a magnetic tape. In some of these VTR's the consecutive tracks are separated by guard bands; and in other VTR's, the recording density is increased by minimizing or even eliminating such guard bands. During normal recording and reproducing modes of operation, the drive apparatus which is used to transport the magnetic tape and the rotary drive apparatus which is used to rotate the magnetic transducers which record/reproduce video signals on the tape are controlled by servo systems, whereby the tape is driven uniformly, the transducers are rotated uniformly, and parallel oblique record tracks are recorded/reproduced.
However, during special modes of reproduction, such as during stop, slow-motion and reverse-motion modes, the tape-drive and rotary-drive servo systems may not be capable of controlling tape and head movement satisfactorily such that a previously recorded record track is scanned accurately during such modes. It is appreciated that, during such special modes of reproduction, the transducers are rotated at the same speed as during the normal mode of reproduction. However, since the magnetic tape is transported at a slower speed, or in the reverse direction, or is stopped completely, the resultant scanning trace of the transducer across the magnetic tape does not coincide with the previously recorded record track. During slow-motion, reverse-motion and stop modes of reproduction, the angle between the resultant scanning trace of the transducers and the longitudinal axis (or tape-movement direction) of the tape is greater than the angle between the pre-recorded track and this axis. Conversely, during a fast-reproduction mode of operation, the scanning trace makes a smaller angle with the longitudinal axis than the pre-recorded track. For proper reproduction of the video signals during such special modes it is important to provide some means by which the angle of the scanning trace is made to coincide with the angle of the pre-recorded track.
In recognition of this need to conform the scanning trace of the transducers during special modes of reproduction with the previously recorded record tracks, various proposals have been made to bring the scanning trace and record track into alignment. For example, in U.S. Pat. Nos. 3,787,616; 4,141,047; and 4,203,140, the use of deflectable members, such as so-called bi-morph leaves, has been proposed, wherein transducers are mounted on such deflectable members which are deflectable in a direction substantially transverse of the scanning trace. When the transducer scans a record track, deviations between the scanning trace and the record track are detected and used to produce tracking error signals. These tracking error signals are, in turn, utilized to generate drive signals that are applied to the deflectable member so as to cause deflection thereof in a direction which brings the transducer into alignment with the record track, thereby nulling the tracking error signal. Typically, the bi-morph leaf which comprises the deflectable member is formed of piezo-ceramic material that is particularly polarized so as to bend in a direction dependent upon the polarity of an electric field produced thereacross in response to the drive signals supplied thereto, the magnitude of such bending being determined by the magnitude of the electric. field.
When the deflectable member bends, the face of the transducer mounted thereon generally is displaced relative to the surface of the magnetic tape so as to form an angle between that surface and the face of the transducer. The size of this angle is a function of the bending, or deflection, of the deflectable member. In an attempt to maintain a constant angle between the face of the transducer and the surface of the tape, it has been proposed, in U.S. Pat. No. 4,099,211, to divide the deflectable member into separate sections, each section being formed of pieze-ceramic material having different polarization directions such that a drive signal supplied to all sections results in an "S" deflection of the member. This allows the transducer to be displaced in a direction generally transversely of the scanning trace so as to correct for tracking errors, while maintaining a substantially constant angle between the face of the transducer and the surface of the magnetic tape.
In the proposals described in all of the aforementioned patents, the deflectable member is secured at one end thereof to a rotary member, such as the rotary drum of a typical HVTR, so as to be cantilevered outward therefrom. Consequently, the maximum bending angle of the deflectable member, which determines the maximum displacement of the transducer, is a function of the length of the bi-morph leaf and the magnitude of the drive signals supplied thereto. While satisfactory bending angles can be attained, during slow-motion and stop-motion reproducing modes with bi-morph leaves of acceptable length to which are supplied drive signals of acceptable magnitudes, substantially greater bending angles must be provided to achieve proper tracking of the transducer during fast-motion and reverse-motion reproducing modes. If the bi-morph leaf is made longer so as to achieve such greater bending angles, the resultant lengthening of the bi-morph leaf is accompanied by a reduction in its natural resonant frequency. Since the speed of response of the bi-morph leaf is a direct function of its natural resonant frequency, such a reduction in natural resonant frequency results in a corresponding reduction in response speed, thereby inhibiting the ability of the bi-morph leaf to correct for tracking errors. Alternatively, if a drive signal of greater magnitude is supplied to the bi-morph leaf in order to increase the bending angle thereof without requiring a longer member, the piezo-ceramic material which constitutes the bi-morph leaf may crack or break. Consequently, there are serious constraints on the maximum bending angle which may be attained by the bi-morph leaf, these constraints being a function of the length of the bi-morph leaf and the magnitude of the drive signals which may be supplied thereto.